However, I'd been gripped by the idea of the Faustian Bargain since high school, specifically because I read a novel called Jack Faust. Jack was one of those books I happened to see at the Public Library (I spent 8-10 hours a week there during the latter days of high school) and grabbed on a whim.
The book pretty well follows the plot you'd expect, and that's a fairly spoiler-free Wiki article---especially since you probably know how Faust ends already. I'm going to briefly provide some marginal spoilers, though it's seriously all stuff you run into in the beginning of the book (at least, as well as I can remember from a book I read over a decade ago).
The one element in the Wiki article that is misleading is the suggestion that the story is a "modernization" of Faust. The jumping off point for the story was the same, but what happened next...well, it was profoundly impactful, and shaped how I've crafted my villains ever since.
Basically, Faust does get a visit from Mephistopheles, only the name is spelled with all manner of symbols tied to math and science. This is becomes the book's Mephistopheles is essentially an astral construct formed of the combined consciousnesses of an entire race of hyper-intelligent aliens. Placed next to humanity (especially pre-Industrial Revolution humanity), these aliens have vastly superior technology but infinitesimal lifespans. They've deduced that their entire race will die out within a small handful of human years, and have decided to bestow some of their wisdom and knowledge on the human race---through Faust---so that it will not be lost.
What's awesome, though, is that the Mephistopheles entity is not doing this out of any sense of altruism. Instead, it wants to do its level best to drive humanity to destruction before, or at the very least shortly after, it expires. Mephistopheles knows that granting Faust advanced scientific knowledge so early will utterly destabilize society, freak people out, and topple nations. It tells him this. In fact, part of the bargain its offering is that Faust has to agree to actually seeing the consequences of his knowledge (through some sort of psychic precognition projection) before it will tell him anything. Faust has to see the ruin to which he will bring the world, accept responsibility for it ahead of time, and then get into bed with the very entity who has expressed such an unwholesome desire for bringing it about.
Obviously, Faust signs the ledger. I'll be honest, other than a scene where a nun has bite marks on her thighs because she likes to get naughty, I don't actually remember much else from the book. It was a good book, and it had an ending, but that's never been what stuck with me.
Mephistopheles, though, is never far from my thoughts. The idea of an entity being so close to omnipotent, yet so utterly petty, is really compelling. You see the same thing in Goethe's Faust too, and it's a significant theme there to watch how bored Faust is with his power. But for me, understanding how to build a monster with that mindset is much more important. DnD has long had a malevolent menagerie of fiends, all striving to capture souls for their designs. However, as much as I love the old-school Larvae as currency concept, it never really justified demons getting involved with mankind to me. They'd come to the world, exert their power at the bidding of some master, wait out its natural lifespan, and then have, in essence, a dollar for their wallet.
Understanding how a creature could be brilliant, and powerful, and petty helped change that. It opened up other emotions that might influence or motivate an entity too; around the same time I read Jack Faust I got deeply into Lovecraft. Getting into Lovecraft while being a young man of mixed Norwegian/African American descent is probably an entry in its own right, but whatever H.P.'s views on miscegenation, the entities he crafted remain so very, very compelling. I've read nearly every "legitimate" Lovecraft story (meaning I haven't sat through everything Derelth passed off as his work) and particularly recall "The Music of Erich Zahn" and Azathoth a window into another way that a character could interact with an entity of greater power. It's only too easy to appropriate the core elements of that story in order to build, say, a Bard whose musical attacks are actually the discordant rhythms necessary to placate some fell and unknowable entity that dogs her steps. If the Bard stops getting into dangerous scrapes, stops sawing at her fiddle until her fingers bleed, then the entity will find the sonic walls of its prison thin enough to reach a glistening psuedopod into our world--surely with dire results.
The first article I ever wrote for publication--internet publication, for the Stygian e-zine produced by the Realms of Evil back when it was my gaming home of choice--discussed consequences of characters who draw power from otherworldly forces. Since I was still playing 3.x at the time, the focus was on how characters learning spells in the Vancian system risked damaging their psyches if the incantations had Infernal, Supernal, or even Draconic sources. It also posited the same risks for any sort of interaction with such creatures (such as by the various Consult... spells). I wanted to suggest that just dealing with that sort of immortal mindset was fundamentally opposed to the way a mortal's mind needs to function, and therefore twisted a lesser race's mind out of whack.
I'm still playing with bargains, power sources, and patrons with agendas. Fourth Edition's presentation of a Warlock who had three pact sources was something I immediately gravitated towards; as I think I may have mentioned in another entry, it's something some of my friends (as were others, and Wizards themselves) already played with in 3.x. I think that it's a shame I see so many Warlocks being rolled without any particular thought to the nature of the relationship between pact-granter and pact-signer, when for me that's probably the most interesting part of the Warlock. My first Warlock was styled as a Sumerian priest (the campaign was heavily focused on its desert setting) who had a monotheistic relationship with a (fictional) deity represented by a particular star. Essentially, he behaved as though he had divine powers granted to him, and was treated thusly by his peers. The harsh, unforgiving brilliance of the star he served helped shape a whole society--one that I wrote as part of his backstory--where the dominant faith wasn't actually worshiping a god, and thus had only limited and costly access to benevolent abilities. All acts of resurrection, warding, healing, and so forth were a result of ritual magic, not granted powers, and thus the priesthood focused on its punishing arm rather than its gentle one.
Similarly, players can tap into capricious Fey lords, but I rarely see them do so. The fact that the Fey pact combines an emphasis on psychic damage with invisibility, debuffs, and teleportation all suggest some frightfully domineering and manipulative masters to me. The tragically underserved Dark pact almost feels like a better fit for Lovecraftian entities than the Star, cosmic ties for the latter nonwithstanding. Despite this, I've never seen someone roll up a Warlock who serves a Cthulan deep-sea entity. My own Dark pact chestnut is a dragonborn whose patrons are three Deva of decadent and sinful pasts. His powers (all taking advantage of that feat which adds necrotic damage to poison damage and vice versa) actually represent him spiritually siphoning away their misdeeds. Their goal is to have him (and those who've come before, and those who are likely to take up the mantle after) bleed away all of their debauchery prior to their deaths, so that they won't rise as Raksha.
The Vestige pact, which I'd expect to be the most promising source of this kind of thing, doesn't seem all that well suited to it in practice. I think it's because the pact is presented so anomalously, serving as a collection of allegiances rather than a single declaration of loyalty with some smaller favor-currying, as the other pacts are. Perhaps if one reskinned the two base vestiges to represent organizations (something like the Scryer/Aldor of Burning Crusade) with some sort of enmity. That way the player juggles versatility in his vestige use with currying greater favor with one side or another; either way, he's even more motivated to learn as many new vestiges as possible in order to have access to powers that won't tie him to the two organizations.
How much of this sort of thought do you put into your characters, dear reader? Do you prefer to turn to the DM for such personalities and considerations, either by expecting them to have it already prepped or by letting them develop it in response to your character concept? Or is the entire idea of bargains with entities much more powerful than your character wholly unappealing?